1. Field of the Invention
The present invention relates to automatic ball check valves operated by gravity and seated by the differential pressure across the ball. More specifically, the invention relates to a ball pushed from its seat along a sloped track by a probe, which probe will be removed by a change in conditions demanding the re-seating of the ball on its seat.
2. Description of the Prior Art
It is often desirable or even necessary to insert probes, such as instrument probes, into an enclosure to detect variables of the environment within the enclosure. The mechanical structure for inserting these probes into the enclosure may include wet or dry tubes, wells or thimbles. One example of these structures is simply a tube which is sealed to the shell of the enclosure for penetration of its interior. An instrument probe incapulated in a dry tube or thimble is guided through this tube to the interior of the enclosure.
The pressure vessel of a nuclear reactor is an example of the enclosures into which dry wells can be installed for receiving instrument probes which remain isolated from the environment in the vessel or in which guide paths can be formed through the vessel which allows instrument probes to be guided into the reactor but which exposes them to the environment within the vessel. A common measurement made by these probes is neutron flux in the core. Since the upper part of the reactor vessel is designed to receive the fuel charging installations, the guide paths are usually provided through the bottom of the vessel and extended into the internal structures which support the fuel assemblies.
The internal pressure of nuclear reactors can be very high. If any of the tubes of the guide paths were to fail, the pressurized contents of the reactor vessel would escape through the failed tubes.
In the past, manually operated valves on the guide tube have been provided. An automatic ball check valve for a dry tube, or thimble, was provided by the system disclosed in U.S. Pat. No. 3,893,651 issued July 8, 1975 to Donald F. Uecker. However, the effectiveness of this system is limited to wells extended vertically downward into a monitored environment. It is true that the patent generally discloses the orientation of the well and valve for extension vertically upward into the environment. However, a more positive, guided travel of the ball valve element is required to insure consistent operation of the valve upon downward withdrawal of the probe.
U.S. Pat. No. 3,769,156 issued Oct. 30, 1973 to Jean Brecy discloses a system for inserting flux-measuring probes upward into the pressure vessel of a nuclear reactor. The sensors are each movable inside a guide tube which slides in a channel. The channel is connected at one end to the vessel bottom, the other end leading to a measuring room. Each channel is provided an adjustable seal between the inner surface of the channel and the outer surface of the channel and the outer surface of its guide tube. No purpose will be served by further analysis of this system as it is evident from a cursory inspection of the disclosure that the seal provided against release of vessel contents is not automatically actuated but is manually adjustable between its two positions. The problem remains of providing upward insertion of instrument probes in the reactor vessels, together with ball valve sealing which is automatic upon failure of the tube externally sealed to the vessel wall.